Major trends in cardiovascular disability, illness and death occur in this country which are neither explained nor predicted, nor are they readily amenable to explanation by retrospective analysis. It is essential to any rational public health policy and plan that an advanced society explain the evolution, at times almost revolution, in chronic disease experience. It is likely that much of the cardiovascular disease experience is influenced by known, or strongly suspected, socioeconomic, environmental, cultural and behavioral factors. These and their physiological manifestations can be measured. It is therefore feasible and desirable to attempt surveillance and analysis of measurable aspects of health behavior, socio-economic indicators, risk characteristics and disease experience - in parallel - within definnd geo-political or trade areas. This application proposes such a monitoring system which would be thorough, systematic and on-going, involving a smaller-than-national unit, the Twin Cities of Minnesota, over the years 1979-83. The potential advantages of this local approach appear to us to be the depth, detail, and control possible, using manageable-sized teams and samples. Moreover, divergent or opposing mortality and morbidity forces, might be less likely operative than with nationwide sampling. Parallel trends or lag periods between socio-cultural changes and disease experience might be detected, and specific hypotheses examined about change. Within such a dedicated research program, disease trends, and risk factor changes would be identified, and methodological approaches developed, for application by other agencies.